1. Field of the Invention
The present invention relates to a Petri dish for cultivating bacteria which is used for isolating bacteria, an enrichment culture, drug susceptibility tests, etc. and a method of inspecting drug susceptibility of bacteria which are isolated from a clinical specimen etc. or purely cultured after isolation by using the Petri dish.
2. Prior Art
When performing bacterial inspection in a hospital, in order to detect the pathogen to which the infectious disease is ascribed, it is necessary to perform operations such as isolation of the culture and enrichment of the bacterial culture from the material to be inspected. Particularly, the results obtained from bacterial inspection are very important since recent trends make it more difficult to identify pathogenic bacteria through clinical diagnosis due to complicated pathologic configurations of infectious diseases.
However, media suitable for growth of bacteria varies depending upon the kind of bacteria. Thus, when screening pathogenic bacteria, an adequate medium must be prepared for the growth of each detectable pathogenic bacteria possibly present. Bacteria which can be found in blood specimens are: staphylococcus, streptococcus, pneumococcus, enterococcus, haemophylus, salmonella, escherichia coli, pseudomonas aerouginosa, anaerobic bacterium, campylobacter, brucella, etc. In order to isolate any of these bacteria, it is usually necesary to prepare media including blood agar medium chocolate agar medium, isolation medium for anaerobic bacterium, medium for enrichment, etc. for every specimen.
Furthermore, salmonella, dysentery bacillus, pathogenic coli, yersinia enterocolitica, klebsiella oxytoca, vibrio, staphylococcus, bacillus cereus, etc. can be detected from feces and the media needed for any of these bacteria include preparations of BTB lactose agar medium, DHL agar medium, SS agar medium, isolation medium for anaerobic bacterium, medium for enrichment, etc.
When producing these media with a conventional Petri dish for cultivating bacteria, it is necessary to heat the media solution for a long time because the media contains agar. Also, the Petri dish must be placed in a horizontal, stationary position in order to facilitate coagulation of the agar. In addition, almost all conventional Petri dishes for cultivating bacteria have one medium prepared per set of Petri dishes. Thus, the number of Petri dishes required for one specimen is increased and inoculations must be performed one at a time for each one.
With the above-disadvantages in mind, a method was conceived wherein several kinds of media are poured separately into a fractionalized (or sectioned) Petri dish. However, the inside of the dish must be provided with partitions since the inoculation procedure must be performed section by section (fraction by fraction). Because the prepared media is different in levels from one section to another, there is no improvement in using a sectioned or fractionalized Petri dish since individual mediums must be prepared for each section and further, since each section must be individually inoculated as in the above-described method using one Petri dish per medium.
Furthermore, in order to prepare various kinds of plate media using a conventional Petri dish for cultivating bacteria, in addition to the necessary complicated steps of preparing the solution, sterilization, separate pouring and coagulation of the components of the media; each operation must be performed in an aseptic atmosphere as possible. Usually, separate pouring of one medium per Petri dish increases the number of Petri dishes necessary for one specimen. Therefore, it is almost impossible to adequately prepare the necessary amount of media required in a hospital's test room where the number of specimens and the kind of bacteria handled are not always constant. For this reason, many facilities make or purchase the estimated amount of media necessary for a predetermined period at one time and use it gradually, storing it in a refrigerator. In this case, since the media when purchased and/or stored is only protected by a fitted lid around the top of the container containing the media, there is a problem in that humidity and/or various bacteria may contaminate the media.
When conventional media is used it must be dried in advance, but media which is in the de-airing state during storage or at the time of purchase has oxygen dissolved in the air during such drying process so that, if anaerobic bacteria are handled, it is necessary to leave the media in an anaerobic chamber after drying.
Also, when applying chemotherapy to bacterial infectious diseases, selecting and using a drug which is most effective in causing the bacterium such as the disease is recommended. Nevertheless, the kind and concentration of the drug which will be effective on the bacteria varies depending on the kind of bacteria, and the recent spread of chemotherapy triggers the appearance of bacterial stock (resistant bacteria) which shows a tolerance to a druge which has been conventionally effective. Therefore, if it is determined that a particular bacterium is causing an infectious disease, it is almost impossible to assume an effective drug. Due to the above, for the purpose of putting therapy which is clinically adequate and reasonable into practice, it should not be forgotten that drug susceptibility inspection is one of the most important procedures when inspecting bacterium.
Methods of inspecting the drug susceptibility of bacteria include the dilution method, the diffusion method, and nephelometry. The agar plate dilution method used an agar medium and the broth dilution method belongs to the dilution method. The sensitive tablet method, the sensitivity disk method, the decantation plate method, and the vertical diffusion method are diffusion methods. In terms of the actual site where the bacteria is inspected, however, the agar plate dilution method and sensitivity disk method are used mainly from an operation-oriented perspective.
The sensitivity disk method is used to make a judgment based upon a biogenetic inhibition circle or inhibition zone of the bacteria to be tested which occurs in response to diffusion of the drug after cultivating the bacteria in the media, the bacteria to be tested is inoculated in advance, when the bacteria does not contain the drug and then a paper disk impregnated with the drug is subsequently placed thereon for a predetermined time. Although this method is widely utilized because it is easily performed and permits testing a plurality of drugs and concentration samples with one Petri dish, it causes thickness, inclination, or the kind of medium on which the disk is placed causes the inhibition circle to flucuate in magnitude so it is likely to lack reproducibility. On the other hand, method using a three-concentration disc, wherein a judgment is made on the basis of only the existence of an inhibition circle, not its magnitude, is sometimes used. However, since the setup width of the drug concentration is larger, such a method is not suitable for measuring the minimum inhibitory concentration (MIC) of the bacteria to be tested.
The agar plate dilution method uses media having a predetermined concentration of the drug contained therein in advance. This is better for reproductibility and can freely set the concentration of the drug. However, since one medium per drug or concentration setup must be used and inoculation must be performed for every media, making this method is complicated.
The purpose of conventional drug susceptibility inspection is to obtain a treating principle regarding the drug concentration at which growth of all of the bacteria is inhibited. However, it disregards the degree of drug susceptibility of the stock of bacteria to be tested corresponding to each drug concentration. In order to obtain more adequate principles as to the infectious disease, which has a tendency to be complicated, it is necessary to collect further detailed information on the bacteria causing such disease.